A known scanner is equipped with an automatic document feeder (ADF). When such a scanner continually scans documents during automatically feeding documents by the ADF, an anomaly, such as a multi-feed, may occur in a state of conveyance and prevent the normal reading of images on the respective documents. For this reason, a known image reading apparatus extracts a side edge of a document from an image data generated by scanning through edge detection processing, or the like, thereby determining whether or not the multi-feed has occurred, based on the extracted state of the side edge.